The performance of a tire which is in particular the grip, the endurance, the wear resistance and the driving comfort is associated with different elements of the tire, such as the choice of crown architecture and the choice and nature of the rubber compounds forming the different parts of the tire. For example, the nature of the rubber compounds forming the tread has an impact on the properties of said tire such as the properties of wear and grip.
Moreover, it is also known by the person skilled in the art that the physical-chemical properties of the rubber compounds vary with the usage of the tire and, in particular, according to the temperature which has, for example, an effect on the properties of the tread of a tire. Thus, during the use of a vehicle, the rubber compounds forming the different parts of the tire such as the bottom areas, the sidewalls and the tread are subjected to stresses which lead to an increase in the temperature of the compounds and thus to variations in the physical-chemical properties of said compounds. It is, for example, known that according to the type of tire and its usage, certain areas of the tire are subjected to stresses such that the temperatures reached may lead to performances of grip or wear of the tire which are not optimal.
It is thus desirable to be able to carry out measurements of temperature or even of a different physical parameter of the tire and in particular of the rubber compounds which form said tire, for example to assist the driver or rider of the vehicle to adapt his or her driving to the conditions and thus optimize the performance of the tire.
For example, under-inflation of a tire, i.e. a pressure of the tire which is lower than nominal pressure, of a passenger vehicle may lead during driving to heating of the shoulders thereof i.e. the axial external ends of the tread.
According to a further example, over-inflation of a tire, i.e. a pressure of the tire which is greater than nominal pressure, of a passenger vehicle or a heavy goods vehicle may lead during driving to heating of the crown thereof i.e. of the central part of the tread.
Moreover, it is known in particular from the document EP 1 275 949 to implant a wireless sensor in the tires to determine the forces or stresses exerted within the tire.
The document EP 0 937 615 discloses the use of wireless surface acoustic wave sensors incorporated in a tire, in particular for measuring the grip of a tire. Such a sensor has the advantage of being able to be interrogated remotely, by radio frequency waves, in a wireless manner, without a close source of energy being necessary. The energy of the interrogation radio waves transmitted by a remote interrogation device is sufficient for the sensor to transmit modified radio waves in response.
It is in particular, therefore, known to position systems for measuring a physical parameter, to determine variations of said physical parameter, in the mounted assemblies of vehicles.
It is also known to use wireless measuring systems, by surface acoustic wave technology or volume acoustic wave technology capable of communicating with an interrogation device attached to the vehicle to indicate a variation of a physical parameter of the tire capable of leading to a modification of the performance of said tire.
The use of this type of system not requiring an energy source, however, requires a limited distance between the measuring system and the interrogation device, in particular to limit the attenuation of the signal corresponding to the measurement.
Furthermore, the conditions of use of this type of system are regulated and are, in particular, limited in terms of maximum radio wave power. These same maximum levels are further limited according to regulations, according to the rate of use of the interrogation device. The principle of measurement on a mounted assembly requires an increased frequency of use of the interrogation device when said interrogation device rotates at increased speed, in particular because the time during which the measuring system passes in front of the antenna of the interrogation device is very short and reduces the probability of obtaining a measurement for each of the interrogations.
It emerges from these observations that the distance between the measuring system associated with the tire and the interrogation device fixed to the vehicle and more precisely the antenna associated with this interrogation device has to be as short as possible.
Tests have been carried out by the applicant on vehicles incorporating an antenna of a device in the wheel housing of the vehicle corresponding to the tire comprising the measuring system.
Tests have shown that it was thus possible to carry out consistent and reproducible measurements. However, it has been shown that in certain conditions of use, in particular associated with climatic conditions, or even according to the sensitivity of the interrogation device, the temperature measurements carried out were not able to be fully exploited, in particular either because the detected signals were too weak or because they were disrupted by other signals on the same frequency band.